The invention concerns a worm gear for transforming a rotary motion into a reciprocating (linear) motion, comprising a threaded spindle which is mounted for rotation in a gear ring nut, a profiled gear ring engaging into a screw thread of the threaded spindle at one peripheral point, which gear ring surrounds the threaded spindle, is arranged eccentric to a spindle axis and fixed on an inner ring of a ball bearing which surrounds the gear ring.
A worm gear of this type is known from EP-PS 0 122 596 and comprises two gear rings with ball bearings whose outer rings are arranged in special rolling bearing receiving elements within a housing. The gear rings surround the threaded spindle. The bearings which serve as a radial support for the gear ring nut on the threaded spindle are needle bearings. The necessity of using a housing and arranging the ball bearings and the rolling bearing receiving elements in the housing results in a structure which is rather complicated on the whole.